The movement of water from source, to point of use, has been an essential element of urban communities and irrigated agriculture since the beginning of time. Canal systems have been widely used for this purpose since the times of Romans and Incas. In arid regions in southwestern United States many older irrigation canals are formed with a compacted earth bottom and gradually sloping sides. In areas of porous materials, compacted earth canals have rates of seepage many times more than canals lined with an impermeable liner.
Over the last fifty years in the arid southwest, clean water has become more expensive to acquire, and the need for secure water containment has increased. During the same time, population increases have placed even heavier reliance upon existing canals systems, greatly reducing the opportunity for taking canals out of service, even for short periods of times.
The common action in the installation of a lining material is to dry out the canal and then quickly lay the impermeable lining. Engineers have tried almost everything to line their canals including clay, bricks, concrete, plastics, geo-membranes and spray on chemicals. During the interim, water must be bypassed around the canal, or the community that depended upon the canal will be without water.
It is therefore the general object of the present invention to provide a method for bypassing water through a section of existing canal in order that the existing canal can be reconstructed in place; and lined one section at a time, while avoiding the cost and difficulty to secure a bypass corridor over lands not occupied by the canal such as in urban or environmentally sensitive areas.
A number of approaches have been used for bypassing water during the lining of a canal or waterway in arid regions.
One approach, is the use of pumps to pump water around the canal such as a recent bypass set-up for the Kern Water District in California. The AP Canal needed to be dry during the beginning of pre-irrigation due to the construction of the new Amtrak Railroad Station. In order to continue to supply its customers, it was necessary to transfer water from one canal to another at two different locations. The first location required a series of bypass pumps totaling 25 cfs and the second series of pumps totaling 35 cfs. This approach was effective but required eight pumps in simultaneous operation. At one location, a problem with debris plugged off the pump suctions necessitating a standing 24 hour pump watch. Albeit relatively small in size, the Kern Water District bypass illustrates some major drawbacks of a pumped bypass system. The drawbacks include: the need for additional room for bypass pipelines, prohibitively high capital cost, and unaffordable ongoing maintenance expenses.
Another approach is to physically construct a parallel canal such as was done in lining the first 49 miles of the Coachella Canal in California in 1980. The existing 123-mile Coachella Canal is a branch of the All-American Canal System conveying water to irrigate 78,530 acres in the Coachella Valley. Prior to 1980, the first 86 miles of the canal were unlined. Seepage losses along the first 49 miles averaged 132,000 ac-ft out of total annual diversions of approximately 500,000 ac-ft. The primary action taken to ensure continued supply of water while lining the Coachella Canal was the construction of a parallel replacement. Obvious drawbacks to this method include: additional right-of-way, and prohibitively expensive replacement of drop structures, siphons, and irrigation turnouts.
An alternative method which avoids the cost of additional right-of-way includes emptying the canal, quickly installing alternative lining materials, and refilling the canal. The most notable materials used, which have consistently failed over time are: woods of various types, asphalt, plastic, concrete or fiberglass. U.S. Pat. No. 3,996,715 to Dowse (1976) discloses a typical one piece building block so shaped as to allow a plurality of identical blocks to be interlocked forming a canal or river lining or for use as a permanent or temporary load bearing surface. Plastic or felt sheets have been proposed which are impregnated with asphalt of various types supposedly sealed to prevent the intrusion of water. Nevertheless in time, all of these methods for rapid installation of alternative lining materials have been found wanting. Wood rots, weeds displace and break apart interlocking concrete blocks, plastic tears, cracks occur in fiberglass, and asphaltic felt undergoes organic attack.
U.S. Pat. No. 1,984,802 to Mallery (1934) discloses a method for diverting the flow around a natural stream as a means for mining the streambed. The method employs conduits of flexible water proof material such as rubberized canvas, or cloth, connected to heavy front openings supported by a cable arraignment. The method has several inherent problems. Without a headwall, the erosive forces will remove soil near bottom and corners of the heavy front openings destabilizing the inlet. Because no provision is made to address the rotational thrust developed when flow is shifted to one side, the force will rotate each individual inlet. The magnitude of erosive and rotational forces will vary with varying water depth and will make sealing the assembly against leakage impractical or impossible when stream water depths exceed more than a few feet. Moreover, the invention requires a steep grade, commonly found in natural streams but absent in canals, to provide sufficient water pressure to maintain the dimensional stability of the conduits, to prevent lateral movement and surging after air pockets have formed due to entrained air, to prevent air-locking as air pockets collect together under a sagging pipe ceiling, and to prevent the collapse of lower conduits from the weight of upper conduits. Because canals have far flatter slopes, the necessary stabilizing water pressures are absent making the invention unsuitable. Finally, the invention is untenable as a canal bypass because no provisions are made for the orderly return of flow from the original stream bed back into another modified stream bed when all work is completed.
Numerous methods have been disclosed using bulkheads or headwalls to stabilize inlets for pipelines, culverts, canals, and rivers. The materials used have been: woods of various types, plastic, steel, concrete and fiberglass structures having an endless variety of shapes. U.S. Pat. No. 2,928,251 to Waring (1960) discloses a typical headwall for an irrigation lateral. The headwall has side and bottom edges which are embedded in the surrounding soil for the purpose of resisting thrust, lowering seepage and preventing erosion. However this headwall, like others in prior art, call for installation under relatively unsaturated conditions. Installation and removal under submerged conditions, particularly for large scale canals, present a whole array of new forces that must be addressed in order to maintain stability and prevent damage to the headwall or canal bed. For example the submerged installation of the Waring invention in a large flowing canal would be problematic because the invention is designed to function as a drop structure, and will do so while being lowered into the canal; introducing rotational forces on the invention, creating erosive forces on the canal bed and inducing disruptive hydrostatic forces within the foundation that are not present during installation under unsaturated conditions. Finally, no provisions are made for the orderly return of flow from the original canal back into another modified canal when all work is completed.
U.S. Pat. No. 3,269,124 to Leathers (1966) discloses a tunnel fishway which aids natural movement of fish through a dam. The invention comprises of a small headwall upstream in the river feeding a major dam. The headwall serves as a transition to a pipe conduit. The conduit runs from the headwall, underneath the dam and reservoir, to a downstream outlet. While the invention recognizes the advantages of a bulkhead and pipeline conduit for the movement of fish in a relatively natural flow pattern, the substantial construction of the headwall, dam, tunnel and outlet does not have the portability necessary for repetitive installation and removal required for lining a canal.
U.S. Pat. No. 4,954,019 to Giroux (1990) discloses a novel approach to solving the problem of canal bypass by conducting the lining operation underwater through use of a large underwater trimming and paving machine. The trimming and paving machine spans the canal and lays down a combination of concrete and PVC while the canal continues in a free flowing condition. The invention is not obvious because construction proceeds under submerged conditions where the invention must address a whole array of new forces. A test of this machine was conducted on the Coachella Canal between Siphons 14 and 15 in 1990. A significant drawback for the underwater trimming and paving machine is the inability to place and compact additional fill material where needed.
Several differing types of theoretical bypasses have been proposed, for example the installation of sheet piling in parallel along the centerline of the canal alignment. Sheet piling is narrow interlocking strips of steel or plastic plate, which are hammered into place; extending down into the bottom of the canal and protruding up out of the water.
One side of the canal could be used while the other side of the canal is allowed to dry-up. The sheet pile method recognizes that a gravity flow bypass is more reliable than a bypass powered by electric or internal combustion engines.
The real life disadvantages to the sheet pile method are significant. The main difficulty is in limiting underflow seepage. The earthen canal, as long as it continues to transport water, will continue to lose water through seepage underflow passing through the canal bottom under the sheet pile and raising the water table on the other side. In order to control underflow, which creates saturated soil conditions making conventional earthwork and concrete lining activities impossible, well points will have to be installed along the length of the canal to dewater the canal subgrade sufficiently for earthwork to proceed. Finally, the sheet pile, once driven, is difficult to remove and relocate.
Accordingly, there is a need for a canal bypass in saturated soils, or submerged conditions, together with portability for repetitive installation, to quickly and reliably transport water around an existing canal which avoids the aforementioned problems in the prior art.